I play far more acoustic these days than when I was a shred metal electric player in the 80's, and I think it does help my electric playing. I'm a lot more precise than I used to be. I use my pinkie far more than I used to, probably partly because I spend a lot more time playing seated (I used to always, always play standing). I'm more creative, and I spend a lot more time playing solo (vs. with a band, or along with records). I've gotten pretty good with several alternate tunings on acoustic, and I use some of them on electric too (I used to always, always play in standard). And I use my fingers a lot more than I used to, playing hybrid on electric too and not just on acoustic.
Downsides? I'm not sure there are any, but I do play slower these days, and I'm much less fluid with single-note runs. I don't think I can blame acoustic for that, and I'm sure I could still shred if I practiced shredding, but I'm not that interested in playing that style anymore. I'd rather spend that time learning more harp guitar.
